help replacing special chars with ascii chars in strings

Hello, I need some help replacing special chars like 'à,é,è,...' in strings with their corresponding ascii char values. I do know the string replace method thus replacing these special chars with normal alphabets, with the example below:

However, I would like to do the same with instead using for example ascii_char(224) instead of replacing with normal alphabets, however I do not know how to proceed exactly if the special character is found in the middle of a string, where I would need to concatenate something like for example: "Holà, comos...", where it should be like "Hol"||ascii_char(224)||", comos..." and it may be possible that other special chars are present in the strings which follow. Thus I would need some help in finding these chars positioning and then add the concatenation sign, ||, and then continue my strings, else if the end of a string, not add the concatenation sign after the ascii_char(). Am using firebird for DBs with IBExpert, and it supports the ascii_char() function. However it is only that my level of programming in delphi is still very low to be able to clearly solve this problem, so pls be patient with me...